It is known, in various human prosthetic applications, to provide an artificial joint in which the movement about the axis of the joint or the relative movement of the joint parts is controlled, especially damped, utilizing a piston-and-cylinder unit in which, during one phase of the movement, a piston rod or other piston portion extends further from a cylinder and during the reverse joint movement, the piston rod is forced back into the cylinder, i.e. the unit is contracted.
The piston defines within the cylinder respective cylinder chambers, in which one of the chambers is traversed by the piston rod whereas another chamber, on the opposite side of the piston, is free from this rod. In the present description, the cylinder chamber which is free from the rod may be referred to as the first cylinder chamber whereas the cylinder chamber through which the rod extends can be referred to as the second cylinder chamber.
Generally speaking a passage is provided between the cylinder chambers and includes a control element for the flow between these chambers The two chambers are also connected to a compensation chamber which serves to compensate for the difference in volumes of the cylinder chambers resulting from the presence of the piston rod in one of them. In the passage between the first cylinder chamber and the compensation chamber, a check valve is provided in an arrangement whereby it blocks flow in the direction of the compensation chamber while in the flow path from the first cylinder chamber to the compensation chamber there is also an adjustable throttle element.
In the conventional hydraulic controller of this type, the adjustable throttle element is arranged in the flow path from the first cylinder chamber to the compensation chamber so that, utilizing this adjustable throttle element, it is only possible to control the movement of the piston rod in the direction of retraction of the piston rod or compaction of the piston-and-cylinder unit. The retraction movement of the piston can thus occur with throttled flow through a gap between the second cylinder chamber provided with the piston rod and the compensation chamber and which is generally not controlled or regulated.
The reverse movement or return movement of the piston thus does not allow for control of the piston-and-cylinder unit.
It has been found that a hydraulic controller, especially for the movement of artificial joints in prostheses should have control of the extension of the joint, corresponding to elongation of the piston-and-cylinder unit, in addition to control of the contraction of the unit if the movement of the joint is to most closely approach natural movement.